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T. W. KEN YON HYDRAULIC SERVOMOTOR SYSTEM May 27, 1952 3 Sheets-Sheet 1 Filed Dec. 22, 1945 7 A 2 A a a w w 4 2 9 4/, M m/W M y 0 1 U I y N w y 2 A (I. 7M 2 0 4 2. m/fl r 7% E r v .H 5 a 1 W 4 1 n4 4 a n no a wad a Q v j INVENTOI?- Him/0]! if [1" 1 011 B I v l l 4 A TORNEY May 27, 1952 T. w. KENYON HYDRAULIC SERVOMOTOR SYSTEM 3 Sheets-Sheet 2 Filed Dec. 22, 1945 INVENTOR ilteadmiffjfiaqan flTTORNEY y 1952 T. w. KENYON 2,598,180

HYDRAULIC SERVOMOTOR SYSTEM Filed Dec. 22, 1945 Sheets-Sheet 3 as 1a 22 21 a4 23 g 2 Z? 32 1 59 INVENTOR.

77 040]? Kffenqan Patented May 27, 1952 UNI TED S TAT-ES PATENT OFFICE HYDRAULIC :SEBVOMQTQB .SXS M Theodore. W. Kenyon, Huntington, N.'Y., assignor,

, by mesne assignments, to the Uni-td sta'tes of America as representeil by-t-he Secretary of the Navy Applieation-Decemher22, 19.45, Serial No. 637,059

Claim 1.1 This invention relates to hydraulic servo-motor systems more particularly for aircraft.

Objects and advantages of the invention will beset forth in part hereinafter and in .part will beiobvious-herefrom,.or maybe learned by practieewith v--th.einvention, the. same being'realized and-attained .by means of the instrumentalities and combinations pointed out in the. appended claims.

'llheinvention-consists in the novel parts, constructions, arrangements, combinations and improvfiments herein shown and described.

TIhe accompanying drawings, referred tohereiii-and constituting-a part hereof, illustrateone embodiment of the invention, and togetherwith -the.. le ri-p eh, s ve to x l the p inc ples oft ven en @b ects of thisinvention are to provide -a .-new,

useful: hydraulic servo mOtor system particularly adapted foruse in- -ai-rc raft which combines extreme i h ness-with com t s of i moving partsptogprovide a new and useful hydraulic se o-.inote s emuhav n a Xt meW rapid 'SP9.. 62 Q:lhQ a plica on of a e isihe i pulse bvi aso ofithe .us i h r li p sure-.-and.sma11 i htw t. m v pa t a d served from the same press;ure source, thereby" to ,efiecteconomiesin weight and cost and facilitate installation and maintenance, and to .provide=,-a .-,me ans of h y-passing the action of the system servomotor to I render it safely. inoperative when not in use.

:Of. the drawings:

vljgigure ,1 is asomewhat diagrammatic View, .Withparts, insection, .of ,a typical and illustrative embodiment. of. a hydraulic servo-motor system inaqcordance withthis invention, depicting .the several elements of, the. system including the signalinpilt control-valve, the transferor relay a veand the hydraulic servo-motor in atypical opera ve ela ion i "Figures '2, 3 and 4 are views insection, respectively, e a t ca a l s rat embod me eta rans o rela va e in ordan ew th this invention, corresponding to the transfer valve-shownimFigure l, the view Figure 2 showingthe valve as itwould appear with its working parts -i-na central or 'neutral p ition corresponding-to a no-signal conditionin the system -of-=Figure lythe views, Figures 3 and 4, showing' the ivalve with. its working 'parts in opposite extremes-of :position corresponding to -maximum signal conditions but of opposite sign in the systemo Fi ure .1 t e, os n O e W g. P r o th a v as sho n in Fi u e. 3 corresponding to t e po i ion r the v irart in e hqll li n Figur a d.

.Eigure h an 7 are ie in se tio of a typical an l ust at e m od m n o a h d aul c servo-motor. in accordance with this invention corresponding to the SGIVOvIl'lOtOI shown in i u 1 the view, i u .5 s o n the servo-motor with its by-pass [slide-valve in open position corresponding to a pressure-0E condition in the system and the views,

Figures (Sand '7, showing the motor withits by- 0 vided ,a high pressure hydraulic servo-motor system including, a transfer valve, a hydraulic servo-motor and suitable means for actuating the transfer valve. The piston .or other movable force .n ember .of theservo-motor, by means of which. motion .or a working effort is adapted to be transmitted to .a lever, cable, wheel, aerodynamic control member or. other member to .be operated, is normally maintainedin a hydraulicallyloalanced oonditionby the application at allti-rnes to one workingfaceof the piston of the full. high. hydraulic working pressure .of the system and by,.the establishment, also, in the servomotor of, a balancing hydraulic'force of lower unit pressure .actingon thepiston over the op.- posite, butlarger area, working face of the piston.

.Also, inaccordance. with the invention, .energising of the servo-motorto effect the transmis'sionoi motion, or a working effect, by the servohnotor pistontov a member to be operated is accomplished by, increasing or. decreasing the hydraulic pressure on the larger .area working face ,only of thepiston..Whilemaintamm the hydraulic force. due to the .pressure actingover the opposite working face at a. constantjo'rsubstantially constant value corresponding to the usual and desired system working pressure. .As a result .of. an. increaseor decrease in .the hydraulic pressure acting .over this. larger area, ,an unbalanced .condition of the oppositely acting hydraulicuforcess-may .be obtained within. the servo-motor piston against internal friction .and the resistance offered by, the member to beoper.- ated. .fihlcethe piston of the servo-motor is norma l in. a. h draul ca y balanced ponditi n by reason of theoppositelyacting equalhydraulic forces, a change-in one of 3 them (disregarding friction) will-effect an'almost instantaneous accelerationoi, or application of force to,--the piston by reason of the high hydraulic pressure employed, .the small size and lightweight of the 3 moving parts and the low volumetric flow, hence low liquid friction, needed for the necessary power. Thus, the speed or response of the servomotor piston is unusually fast by reason of this novel combination of features.

In order to upset the balance of hydraulic forces acting on the servo-motor piston for the purpose of effecting movement of the servo-motor piston in one direction or the other, or to restore or maintain the balance of such forces in response to the unbalancing action of an external force, provision is made for increasing or decreasing at will the hydraulic pressure on the larger area working face of the piston while maintaining the pressure on the smaller area working face substantially constant. To this end and in accordance with the invention, transfer valve means are provided normally hydraulically balanced and functioning to seal the servo-motor against loss of hydraulic liquid from the larger area working face side of the servo-motor piston, the valve means being operable and so constructed and arranged however as to permit hydraulic fluid to be supplied to or discharged from the larger area side of the piston without altering or substantially altering the hydraulic pressure on the smaller area working face of the piston. The embodied transfer valve means may, if desired, be actuated by any suitable mechanical, hydraulic or electric means but is preferably fashioned so as to be pneumatically energisable by means of a suitable external control valve through the medium of which an operating pneumatic signal may be supplied to the transfer valve means to actuate it so as to obtain the desired pressure increase or decrease, or to maintain the desired balance of hydraulic forces in the servomotor.

It will be understood that the foregoing general description and the following detailed description as well are exemplary and explanatory of the invention but are not restrictive thereof.

Referring now more particularly to the embodiment of the invention shown in the accompanying drawings, there is depicted in Figure 1 a hydraulic servo-motor system in accordance with the invention such as is particularly adapted for use in aircraft for operating the elevators, ailerons and/or rudders of the aircraft in response to controlling impulses generated by a gyroscope or other base-line indicating device. As shown, a hydraulic servo-motor i is operatively coupled by hydraulic lines H and 12 to a transfer valve i3 which in turn is operatively coupled by pneumatic lines 14 and 15 to an air signal control valve l6 having the air inlet and eduction lines I! and t8, respectively.

The system servo-motor 10 as here preferably embodied comprises a cylinder or casing member [9, which is preferably a casting of a strong but light metal e. g. aluminium alloy, capable of withstanding high hydraulic pressures in the order, for example, of 3000 pounds per square inch. The cylinder member [9 is provided with a bore containing a relatively thin cylindrical liner 2|, preferably of stainless steel, offering suitable resistance to frictional wear. The liner 2| is annularly spaced from the casing I9 throughout a major portion of its length so as to provide an annular space 22 for liquid therebetween and one end of the liner is snugly lodged in a socket 23 formed by a reduced diameter section of the bore 20. The opposite end of the liner is firmly engaged by a centrally apertured gland member 24 having annular packing rings 25 and 26 by which the gland member 24 is removably tightly sealed to the casing is and to piston rod 21, respectively. A split ring 28 engages the 'ca'sing 19 for holding the gland member 24 in the casing. Orifices 29 in the liner 2! adjacent the gland member at suitably spaced intervals provide ports for the flow of liquid between the annular space 22 and the bore 29 and an annular shoulder 30 extends inwardly from the liner adjacent the orifices 29 to fix the extended position of the piston 31 in the bore 20 as shown in Figure 7.

The piston 3! is mounted on the piston rod 21 at one end thereof and concentrically therewith and carries annular gasket means 3| by which a sliding seal is effected between the piston and liner. The working faces 32 and 33 of the piston 3| are of unequal area by reason of piston rod 27, the piston and piston rod being proportioned to each other so that the effective area of the working face 33 is less than and in desired proportion to the effective area of the Working face 32. Preferably, the area of the working face 32 is twice that of the working face 33 although other suitable proportions may be provided for as hereinafter described.

VJhen the area of the working face 32 is twice the area of the face 33, the piston 3| will be in hydraulic balance where a unit hydraulic pressure on the face 32 is one-half the unit hydraulic pressure on the face 33. If the unit hydraulic pressure on the face 32 equals the unit hydraulic pressure on the smaller face 33, or is reduced to zero, the hydraulic force tending to move the piston to the right in the first case,

' and to the left in the second case, will be the same. Similarly, if the ratio of the areas is greater than 2 to 1 as, for example, 5 to 1, the

" piston 31 will be in hydraulic balance in such case when the unit hydraulic pressure on the large area face 32 is one-fifth the unit hydraulic pressure on the smaller area face 33. However, if the unit hydraulic pressure on the face 32 equals the unit hydraulic pressure on the smaller face 33, or is reduced to zero, the hydraulic force tending to move the piston to the right in the first case will be four times as reat as that tending to move it to the left in the second case. Because of this peculiarly advantageous relationship, it becomes possible to adapt the servo-motor for use where a greater hydraulic force is required in one direction of the piston motion than in the opposite direction as, for example, in lowering and raising aircraft landing gear, wing flaps or the like, simply by establishing the necessary ratio of areas of the working faces in the first instance.

In order to maintain a fluid space between the working face 32 of the piston and the end wall 34 of the bore 20 in the fully retracted position of the piston, as shown in Figure 6, the piston is provided with a spacing member 35 which may be of cylindrical contour as shown and co-axial with the piston rod 21 and it will be apparent that the area of the end of the member constitutes a part of the area of the working face 32 of the piston.

The cylinder member [9 is preferably provided at one end with a laterally extending slide-valve housing 36 preferably integral therewith through which leads a passage 3'! connecting the annular passage 22 and the bore 20 at one side of the piston 33 with a terminal port 38 in the housing surface. Another passage 39 leads directly from the bore 20 at the greater area working face side of the piston through the valve housing to a steered surface'portd-fl. I-t Will be apparent that- -hydraulic liquid *may be supplied through the passage 37, the passage 22 andthe-severalports 29 to the smallenareaworking tace 33 of the piston and may be separately independently F supplied through the passage 39 to the larger area workingface 32 of-the piston. 'l he pipes l and l2 are connected td-the cylindermember 13 atthe terminal ports 49 and 38, respectively, of the passages- 39- and 31, respectively, I and :may have a threaded connection therewithan'd -are connected thereto in---s'ui=table fashion effective to forms liquid-tight jbint under high hydraulic pressures.

V alve '=means' are provided for -au-t'omatically cohnecting-the' bore spaces onopposite sides of the pist'on 3.! to each other when-the hydraulic pressure -on'- the working-face 33 of t'he-piston falls=to-a selected minimum value so -that the piston imay be' freely slidable in'its cylinder. As here preferably embodied, a' slide valve 4| having pistons 13 and 4-6 is reciprocably mounted in a valvechamber I52 in the valve housing '36, .one end .of the valve-chamber connecting'with the liquid passage '31 so that hydraulic. pressure'of the liquid in the passage 31 may actagainst the valve piston ito .force-Jthe valve to the valvecl'osedypcsiti-on shown inE-igures 1.,::6,and.7.. .lhe valve 43, zin' the valve-closed position; as shown in- .Eigu'res .1, :6 land [coversone :end 10f a lay-pass passage'flfliwhosei other end terminates in-thepas'sage :31. As hydraulic pressure onthe piston 43'is:-reduced,':the valve 41 is-moved-bya spring, acting against .a pistcn atrthe other end of-the valveyto za=valve-ropenz1position, as I bodied: comprises front and rear body asections shown in Figure- 5. The .pistons'w43 and Mere :spaced-ly connected "by: a stem member 41 of reduced "diameter. :providingan annular space 43 therebetween forming in effect an enlarged chamber portion 7 the passage 39. The piston 46-isprovided with -.-suitable gasket means '49 forming a-sliding seal with the wall of the valve chamber 42 against-- leakage from the valve housing around the valve springretaining member 5!]. An-annu-lar-shoulder 51 extending inwardly from the valve housing BG-into the valve chamber- 32 provides a limitstop against'which the-piston 43-abuts-in the valve-open position, as shownin Fi re It will .be-apparehtthat starting with the presa sure-off condition shown in Figure 5, hydraulic liqu id supplied to the servo-motor via the passages 3?! and tfiwill till the annular passage 22 and the bore .23. The--liquid entering through thepas-sage-S-i' acts -agai-nst thepi-ston 3310 over: come theforce of the .spri-ng tia with themcsult that the valve 64 willbemoved-to thevalveclosed position shown :in Figures '6- and l7+thus blocking the bv-pass passage M- which enables the movement of thei-piston-in the pressure-off condition. A=balance :of thehjydraulic forces actingonthe working faces 32 and "33 of the piston 3=l .may be achieved suitably proportioning @the pressures on the opposite .side of the piston to each ether to" compensate i for the" difference in area of' the Working-faces. Preferably, -the area of thewoi lring face 32' of the piston "3 is twice that ot the working face 33 a nd the unit hydraulic pressure of the liquid supplied throug-ri- -the passage 31 is preferably tw ioe' that of -the liquid supplied through the passage-3h. It '\vill=';be apparent that by increasingthe' unit .pressu-re of theliquid entering through the passage 39, the piston-3 maybe moved fromthe'pos'ition shown in Figure '6 to the position "shown-in Figure 7, the

unitpressure of the hydraulic liquidiin the opposite side of 'thepiston being maintained constant. Similarly, by reducing the unitpressureon the working face sz, the piston maybemoved. from right to left as Viewed inFigure '7. It will therefore be clearly apparent that because thelunit pressureon the highpressure side of the servomotor -is maintained constant, a numbienof servomotor unitemaybe connected together-fin. a. barn: for individual operation bymanifolding. the :high pressure sideof each i'to ac'ommon headeri..-and supplying the :low pressure Lside ofieachhydraulic unit-with hydraulic liquid bya separate .lineito each unit. -:In th is way, :the piping "required: for the operation .of-a p1uralityo'f servo-motoriunits may :besubstantially reduced vwith concomitant savings in Weight and" cost and'imanifestsimplifica'tion of installation and maintenance problems.

For the purpose. of. mounting the. .unit with 1 a vii 't'oiits use inaircraft; so as .t.o"be-.zseh.aligning; the:cy-linder membei" it: may be provided with an .e-ye-orllug member 52 as bestshown in Figure 5, which maywthreadedly engage: the'cylin-der me'm ber' -l g. at one end thereof .andzis: pro-' vided with. a self-aligning ball bearing fittingzfifi for attaching the unit .to. amounting shaft .Of the aircraftstructure. Similarly, .the piston rod.. 2'l may 'terminatetin' a removable fitting. Etthreadi edlylengiaging the .rodand provided with a. selfaligning ball bearing unit 5.5 for couplingithe piston rod to a rock-shaft orother memher'to he operated.

The transfer valve t3 as here preferably-lem- 63 and 5! respectively, as are best seeniin Figures 1 :to tin-elusive. The-respective body .sectionsare firmly :but removably secured to eachother .as'iby means of. a circular row of'screws "52. passing through'one section into threaded engagement with the other section. The opposing fElBBSIOf the bodytsections are fashioned to provide .a valve chamber preferably cylindrical, within which lSdlSIJOSBd in parta normally hydraulically-halancedhydraulic valve member 54. The valve member "6!; is shown in'its neutral position:in Figure .12 and in extreme oppositely displaced positions'in Figures .3 and 4, the position shown in Figure 8 corresponding to that of Figure 1,;as

v will be explained more fully hereinafter.

The valve member t l is preferably provided with oppositely extending and preferably 1coa'xially aligned piston members 65 and x35, preferably ofcylindricalcontcur, which are freely, slidably received in preferably co-axially aligned valve-seats or cylinders 6? and 438, respectively, of complementary contour and diameter provided inithe valve body sections 63 and 6 1, respectively. The end-faces 6Q and 79 of the piston'members EE- ahdhfi, respectively, constitute thework'ing faces-ofthe pistons and in accordance with the invent-ion, these faces are of unequal areas "corresponding to the ratio of areas of the working faces-32 and 33 of the servo-motor piston 3 i. To this end-the area of the working face 69 of the valve piston member 55 is larger'than the area of the'working face it} of the valve piston member '55, the ratio of areas preferably-beingin the order of two'to one as inthecase of the'servomotor 16. Hydraulic pressure liquid is adapted to be supplied to theWorking-faces and '13 through passages H and I2, respectivelyyprovided in the-body sections Bi) and 6!, respectively. In accordance with the invention, hydraulic liquid'may be supplied to "the passage H from'the pipe II and may be supplied to the passage I2 from the pipe I2 which latter is adapted to be supplied with the high pressure hydraulic liquid through a main feed pipe 13 from a high pressure pump or high pressure liquid reservoir (not shown).

The valve member 64 additionally comprises means for shifting the valve member in either direction from its neutral position in response to an external energising force or impulse as, for example, from the signal control valve I6. As here preferably embodied, a series of highly flexible, fluid-impervious diaphragm members I5, I6 and I1 are secured concentrically of each to the valve member and in axially spaced relation therealong and are fixedly secured at their respective marginal portions in relation to the valve body sections 60 and GI as will appear more fully hereinafter. More specifically, the diaphragm member I5, preferably of circular contour, is clamped between opposingcircular flange members I8 and 19 of the valve member and midway between the diaphragm members I6 and 11. The flange clamping members I8 and 19 may be secured to each other and to the diaphragm member I5 by screws or rivets (not shown) or may be adhesively bonded to the diaphragm member I5. Each flange member is preferably formed integrally with a concentric axially extending clamping boss, the fiange member 19 having the boss 80 and the flange member I9 having the boss 8|. The bosses 30 and SI are also preferably of cylindrical contour and disposed to co-act with valve piston heads 82 and 83, respectively, to clamp the diaphragm members I6 and 11 between them. Thus, the boss 80 and piston head 82 clamp the diaphragm member It between them, being coupled to each other and to the diaphragm member by means of screws or rivets (not shown) or preferably by adhesive bonding to the diaphragm members with which they are concentric. The boss 8I, diaphragm member I! and piston head 83 similarly co-act. Thus, the valve member 64 will be seen to be composed of a plurality of separate elements correlated and coupled to each other and integrated into a unit reciprocable in either direction in the valve piston seats 67 and58 and the valve chamber 63.

The valv chamber 03 is preferably of cylindrical contour having parallel end walls 84 and 85 recessed to form stepped, concentric, preferably cylindrical wells 80 and 81, respectively, for accommodating the valve piston heads 82 and 83, respectively, as the valve member is displaced to right or left from its neutral position. The extent of axial movement of the valve member 64 is confined to fixed limits by the provision of an annular slot 88 extending radially outwardly from the valve chamber into which extend the valve flanges I8 and I9 and which is partitioned centrally by the diaphragm member I5. The opposite parallel end walls 89 and 90 of the slot provide opposing abutments against which the flange members 78 and I9 may contact as the valve member 64 is displaced to right or left and thus serve to limit the displacement of the valve member in accordance with the predetermined operating characteristics of the valve.

The diaphragm member I5 is received at its outer circumferential margin between the body sections 60 and GI so as to be held securely thereby and therebetween. Likewise, the diaphragm members I6 and H of smaller outside diameter are clamped at their outer circumfer- 8 ential margins to the body sections 60 and 6|, respectively, as by means of annular clamping rings 9| and 92, respectively.

It will be apparent that the diaphragms I6 and- TI form with the central diaphragm I5, a pair of hermetically sealed chambers 93 and 94 from which passages 95 and 96, respectively, lead to the outer surface of the body sections 60 and GI, respectively, where they are sealingly connected to air lines I4 and I5, respectively, of the signal control valve I6.

Likewise, the diaphragm members I6 and 11 form with the body sections 60 and GI, respectively, a pair of hermetically sealed compartments 91 and 98 which are connected to each other by a passage 99 leading through the body sections and to the outer surface of th body section 60 where connection is made to a hydraulic liquid return line I00 leading to the liquid sump or reservoir (not shown) of the hydraulic system. Hydraulic liquid which forces its Way past the valve pistons 65 and 66 under the hydraulic pressures employed, discharges into the drainage compartments 9? and 98, respectively, from which it may return to the system reservoir through the pipe I00.

The valve piston cylinders 6'! and 68 are provided with ports It and I02, respectively, both of which are normally just covered and closed by the valve pistons 65 and 66 when the valve member 64 is in the neutral position shown in Figure 2. The ports MI and I02 are suitably located along the length of the respective cylinders 61 and 68 and the valve piston members 65 and 06 are of such length that as the valve member- 60 is moved in one direction or the other from the neutral position, it will immediately start to un-- cover one or the other of the ports IOI and I02, depending upon the direction it is moved. The port IOI is connected by a passage I03 to the return passage 99 and thence to the system sump by the pipe I00. The port I02 is connected by a bleed passage I04 to the valve piston cylinder 61 at the working face end of the valve piston 65. Thus, as shown in Figure 3, movement of the valve member 64 to the right from the neutral position shown in Figure 2, will uncover the port I02 in part or in whole and result in the formation of a continuous passage for liquid from the entrance port of the passage I2, through the passage I04 to the exit port of the passage II. Hence, hydraulic liquid supplied to the passage 12 through the pipes I3 and I2 can not only act against the working face I0 of the piston member 66, but can also act against the relatively large area working face 69 of the valve piston member 65 and against the relatively large area working face 32 of the servo-motor piston 3|, so long as the port I02 is uncovered. Similarly, when the valve member 64 is moved from its neutral position to the left, as shown in Figure 4, the port IOI will be uncovered in whole or in part and result in the formation of a continuous liquid passage from the entrance port of the liquid passage II through the passage I03 to the exit port of the passage 99. Hence, hydraulic liquid supplied to the passage 'II by the pipe II may flow directly to the system return sump through the return line I00.

The signal control valve l6 may be of any suitable type operative to establish a differential pneumatic pressure through the pipes I4 and I5 in the chambers 93-424 for effecting a movement of the valve member 64 in the desired direction and of the desired magnitude. As here preferablyembodied, a vane III! shown in dotted lines ismounted in a casing III for angular movement in either direction. fromfa neutral position in alignment. with the air inlet and eduction pipes I]; and I8. Preferably, the pipe I8 is connected to a. vacuum pump (notshown) and the pipe I1 is open to the atmosphere, although it is obvious thatair under-pressuremay be supplied to the casing: through the pipe I1, and the pipe I8 then arranged to discharge tothe atmosphere. With the. vane III] in the dotted line position shown, the chamber 94 will be subject to a greater fluid pressure thanthe chamber 93- and, byreason of the pressure difference acting, onthe diaphragm member-15,- the valve member 64 will be caused to moveto the right asshown in Figures 1 and 3. Obviously. the valve member may be displaced in the-opposite direction from its neutral position by angular movement of the vanein the opposite direction from its neutral position. In either casethe magnitude of theinitialdisplacement of the valvemember 64 will be-proportioned in part" to the duration and amount of displacement of the vane I I0, the vane in turn being controlled manually orautomatically, as for example, by precession-of a displacement or rate gyroscope, or a..combination thereof, in response to a course and/or attitude change of a=dirigible vehicle.

In'the operation of the hydraulic servo-motor shownin-Figure 1, the systemis first filled with hydraulic liquid in'the required amount with .the liquid in thesupply pipe 13 at the desired working pressure-of for example, 1000-3000 pounds per square inch. Under these conditions, the unit hydraulicpressure exerted by the-liquid on the smaller area working face. 33 of the servo-motor piston 3| and on the smaller area WOrking face I0 of the valve piston member; 64 is the same. The resultinghydraulic force acting on they working face 33 of the piston 3| is balanced by an equal andiopposite hydraulicforce on the working face 3-2;,but because of thelarger area of the working face 32, the unit hydraulic pressure of the liquid acting on the working face 32 will be at a lower value of, preferably, half the unit hydraulic pressure on the opposite side of the piston. The same condition will exist with respect to the unit hydraulic pressure on the working face 69 of the valve pistonmember 65. Hence, the servo-motor piston 3| and the valve member 64 will be in hydraulic balance, with the piston 3| at rest and the valve member 64 at rest in the neutral position showninFigure 2. Assuming now for example that the vane I I0 of the signal control valve 6 is displaced from a neutral position in alignment:

with the ports of theair lines I! and I8 to a position'gsuch as is shown in Figure 1, the suction applie.d;through the pipe I8 will be communicated to thechamber 93 of the transfer valve and atmospheric or substantially atmospheric pressure will be established in the chamber 94. As a consequence of the differential pressure, the valve member will be displaced to the right and, assuming the. differential control signal to be of suificient strength, to the extreme position shown in Figures'l and 3. The movement of the valve member will result in the uncovering of the bleed port I 02 andpermit the full system pressure to be applied through the passage I04 to the working face 69 of the valve piston member and to the corresponding working face 32 of the servo-motor piston 3|. The resulting unbalanced hydraulic force acting on the working face 32 of the piston 3| will substantially instantly cause the piston 3| to move 'rapidly-to'theright asviewed in Figure 1 against the resistance offered by whatever member to which the piston rod 21 is connected. If that member be, for example, the rudder of an aircraft in flight, the rudder will be displaced until the dynamic forces acting thereonattain a value at which the unbalanced hydraulic force acting on the working face 32; is balanced therebyand the piston 3| thereby brought to-rest.

The pneumatic displacement force which caused the initial displacement of the valve member 64 is opposed and balanced by the'opposing hydraulic force resulting from the increase in hydraulic pressure on the working face 69-of the valve piston member 55- as the port I02 is uncovered. This excess of hydraulic force on the working face 69 will remain, even though the servo-motor piston 3| has come to restunder the'balanced forces, until the differential signal pressure-in the chambers 9394 is caused to decay as by initiating restoration of the vane IIO toward its no-sig-nal position. A the signal is caused to decay, the pneumatic displacement force decreases, the-balance between the displacement force andthe excess of hydraulicforce on the working facets-is upset and the valve member 64 is moved. hydraulically toward itsneutral position. When the signal has fully decayed, the valve member will have returned to its neutral position, theport I02 will have been coveredagain and the valve member 64 will be in the neutral position shown in'Figure, 2. It willbe remembered, however, that it was assumed that the pistons] in its; initial displacement wasresisted by the dynamic forces acting on an aircraft control member (not shown) This resistive force added to the hydraulic force acting onthe, working ,face 33 was'balanced by theincreased hydraulic force actin on the working face 32 of the pistonresultingfrom the application of the system pressure to the working face 32. Hence, as the hydraulic pressure on the workingface 32 isdecreased byv the covering of the port I02, the dynamic pressure exerted by the control member will continue, to act through the hydraulic liquid in the pipe I I on the working face 69 of the valve piston member 65 and cause the valve member 64to move to the left, as viewed in Figure 4, thus uncovering the port IOI. The hydraulic liquid may in consequence flow through the passages I03, 99 and the system return line I00 to the sump or reservoir not shown to relieve the excess of hydraulic pressure on the working face 63. As the resistive force of the control member on the piston 3| decays through return of the control member to a neutral position, the decreasing unbalanced hydraulic force acting on the piston member 65 permits the valve member 64 to return to its normal neutral condition with the hydraulic forces on the valve member Bland the piston member 3| in balance.

It will therefore be apparent that displacement of the valve member 64 to the left, as shown in Figure 4, by actuation of the signal vane III! in a clockwise direction, as viewed in Figure -1,,v will uncover the port I BI and thus relieve the balancing hydraulic pressure of the liquid on the working face 32 of the piston. So long as this condition is maintained, the full system pressure acting on the working face 33 will function to move the piston 3| to the left, as viewed in Figures until the hydraulic pressure differential is balanced as before by the dynamic pressure acting on the control member to which the piston rod 21 is connected. When this condition is attained, the piston 3| will come to rest and remain at rest as thevalve member as is returned to its neutral position by a decay of the control valve signal. As the pressure on the working face 61 under these conditions will be less than the pressure on the working face 10, the valve member 64 will be automatically displaced to the right, as viewed in Figure 3, the port [02 uncovered and the hydraulic pressure acting on the working face 32 built up. As it builds up, the dynamic force on the control member will return the latterto its neutral position, and hydraulic balance will again be achieved in respect of the piston 3| and valve member 64.

It will be obvious that if the piston 2'! be connected to a member offering only frictional resistance to movement, the movement will continue within the limit of movement of the piston 3! until the valve member is returned to its normal neutral position. Return of the piston to its starting position may be effected by movement of the valve member in the opposite direction.

a shaft journalled for limited angular movement a in a cylindrical casing so that the movement of the vane by unbalanced hydraulic forces may rotate the shaft directly. In such case, the shaft may be that upon which a rudder, elevator, aileron, or other control member is mounted, thereby eliminating, or reducing in substantial measure, multiple links, cables, sheaves, push rods and such motion transmitting devices between the servo-motor and the control member and effecting advantageous economies in cost, weight maintenance and the like,

The invention in its broader aspects is not limited to the specific mechanisms shown and described but departures may be made therefrom within the scope of the accompanying claims without departing from the principles of the invention and without sacrificing its chief advantage.

What I claim is:

1. In a hydraulic servo-motor system for use with a differential pneumatic signal generator and having a source of hydraulic liquid under high pressure and a sump; the combination of a valve piston and a servo-motor piston each having a pair of working faces of unequal area, the ratio of areas of the pairs of working faces being substantially the same; hydraulic circuit forming means including a pair of cylinder means slidably receiving said pistons respectively, said circuit forming means comprising a high pressure leg between the pair of working faces of correspondingly small area having an induction port through which hydraulic liquid is adapted to be supplied to said leg from said high pressure source, a low pressure leg connecting the pair of working faces of correspondingly large area and having an eduction port normally covered by said valve piston through which hydraulic liquid is adapted to be discharged to said sump, and a pressure-equalizing leg for connecting the high and low pressure legs to each other having a terminus in said low pressure leg and an entrance port in said high pressure leg, said entrance port being normally covered by said valve piston; and means responsive to the difierential pneumatic signal for shifting said valve piston in one direction in its associated cylinder means to uncover said entrance pcrt of said pressure-equalizing leg and for shifting said valve piston in the opposite direction to uncover the eduction port of said low pressure leg, said valve piston shifting means including a pneumatically actuated flexible diaphragm attached to said valve piston.

2. The hydraulic servo-motor system of claim 1 in which said valve piston shifting means further includes a signal control valve, duct means connecting said valve and said pneumatically actuated diaphragm, said signal control valve establishing a differential pneumatic pressure on opposite sides of said diaphragm in response to the differential signal.

3. In a hydraulic servo-motor system having a source of hydraulic liquid under high pressure and a low pressure sump, the combination of a servo-motor having a piston with working faces of unequal area, a transfer valve having a valve piston with working faces of unequal area and of the same ratio of areas as the working faces of said servo-motor piston, separate hydraulic legs between the corresponding pairs of working faces, a pressure-equalizing leg in said transfer valve for connecting said legs to each other at will and a discharge port in the hydraulic'leg between the large area pair of working faces, said pressure equalizing leg and said discharge port being normally closed by said valve piston and selectively openable thereby, conduit means connecting said source of high pressure hydraulic liquid with the hydraulic leg between the small area working faces and connecting said eduction port to said sump, said transfer valve including a pair of coaxial cylinder portions of unequal diameter and an intermediate cylinder portion of a larger diameter than said coaxial portions and connecting the latter, said valve piston traversing said intermediate portion and having oppositely extending piston members slidably received in and complementary to said coaxial portions, and pneumatically actuated piston shifting means mounted in said intermediate portion and attached to said oppositely extending piston members.

4. A valve comprising a cylinder portion, a piston therein having a pair of opposed working faces of unequal area, separate ducts for supplying hydraulic liquid to said working faces, a duct for connecting said first mentioned ducts, and a duct for venting liquid from one of said supply ducts, said connecting and venting ducts being normally closed by said piston; and, pneumatic-' ally actuated means for moving said piston in opposite directions to selectively open one or the other of said connecting and venting ducts, said last named means including a flexible diaphragm attached to said valve piston.

5. A transfer valve comprising a body portion having cylinders of unequal diameter connected by a seepage chamber, a pair of piston members complementary to and slidably received in said cylinders, flexible diaphragm members traversing said chamber between said piston members and said body portion and dividing said chamber into pairs of separate compartments, the compartments of one of said pairs serving to collect seepage liquid from said cylinders, air ducts for establishing a pressure difierential in the compartments of the other of said pairs. a duct for educting seepage hydraulic liquid from said collecting compartments; separate ducts for supplying hydraulic liquid separately to each of said cylinders, a pressure equalizing duct for connecting said supply ducts at will, and a venting duct for venting the larger diameter cylinder and its supply duct through said body portion, said pressure equalizing duct and said venting duct being normally closed by said piston members.

6. A transfer valve comprising a body portion having coaxial cylinders of unequal diameter connected by a chamber of substantially larger diameter, each said cylinder having a, port in its cylinder wall, a valve piston comprising a pair of coaxial piston members each complementary to and slidably received in one of said cylinders and covering the port therein, flexible diaphragm members in said chamber flexibly connecting said body portion and said valve piston and dividing said chamber into a pair of air compartments for effecting reciprocation of said valve member by differential pressure and a pair of intercommunicating seepage compartments for receiving seepage hydraulic fluid discharged from said cylinders, said air compartments communicating through separate ducts with separate openings in the surface of said body portion, separate ducts for supplying hydraulic liquid separately to the respective cylinders, a pressure-equalizing duct connecting the port in the smaller diameter cylinder with the larger cylinder supply duct, and a vent duct connecting the port in the larger cylinder with a separate opening in the surface of said body portion and providing communication between said opening and said seepage compartments.

'7. A valve comprising a body member having a chamber therein, said chamber portion including a pair of spaced cylinder means of unequal diameter connected by a larger intermediate cylinder means, a valve piston in said chamber having a pair of oppositely extending piston members complementary to and slidably received in said spaced cylinder portions, said piston members having unequal working areas, separate ducts for supplying hydraulic fluid under high and low pressures, respectively, to the small and large area working faces, respectively, a duct for equalizing the pressures in said supply ducts, a duct for releasing the pressure in said low pressure duct, said pressure equalizing and releasing ducts being normally closed by said piston, and pneumatically operated means mounted in said intermediate cylinder means and operatively connected to said valve piston for moving said piston members to selectively uncover either one or the other of said pressure equalizing and releasing ducts.

8. In a hydraulic servo-motor system for use with a differential pneumatic signal generator and having a source of hydraulic fluid under high pressure and a sump; the combination of a valve piston and a servo-motor piston each having a pair of working faces of unequal area, the ratio of areas of the pairs of working faces being substantially the same, hydraulic circuit forming means including a pair of cylinder means slidably receiving each of said pistons, said circuit forming means further including a high pressure leg between the pair of working faces of correspondingly small area having an induction port through which hydraulic liquid is adapted to be supplied to said leg from said high pressure source, a low pressure leg connecting the pair of working faces of correspondingly large area and having an eduction port normally covered by said valve piston through which hydraulic fluid is adapted to be discharged to said sump, and a pressure equalizing leg for connecting the high and low pressure legs to each other having a terminus in said low pressure leg and an entrance port in said high pressure leg, said entrance port being normally covered by said valve piston, and pneumatically actuated valve shifting means mounted on said valve piston intermediate the working faces thereof, responsive to the differential pneumatic signal, for shifting said valve piston members in one direction to uncover said entrance port of said pressure equalizing leg and for shifting said valve piston members in the opposite direction to uncover the eduction port of said low pressure leg.

9. In a servo-motor system having a source of hydraulic fluid under high pressure and a sump, a servo-motor including a piston slidably mounted in a cylinder, said piston having a pair of working faces of unequal area, high pressure conduit means connecting said high pressure source with the smaller of said working faces, low pressure conduit means connecting said sump and the larger of said working faces, pressure equalizing conduit means connecting said high pressure conduit means and said low pressure conduit means, first-mentioned valve .means mounted in and normally closing said pressure equalizing leg to prevent communication of the low pressure fluid and high pressure fluid, second-mentioned valve means in said low pressure conduit means to normally prevent the fluid therein from flowing to said sump, and pneumatically actuated means operatively connected to said first and second mentioned valve means for selectively opening or closing said first and second-mentioned valve means, so that when the first-mentioned valve means is opened the pressure in said low pressure conduit means equalizes with that in said high pressure conduit means thus providing an unbalance in the forces applied to said unequal area working faces causing the piston to move in one direction, and when the first-mentioned valve means is closed and the second-mentioned valve means is opened the high pressure fluid in said low pressure conduit means is permitted to communicate with said sump thus decreasing the force differential on said unequal working faces causing said piston to move in the opposite direction.

10. The servo-motor system of claim 9 wherein said pneumatically actuated means includes a flexible diaphragm connected to said valve means and mounted in a cylinder intermediate the ends thereof, and a signal control valve for supplying a differential pneumatic pressure to opposite sides of said flexiblediaphragm.

THEODORE W. KENYON.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,431,101 Dineen Oct. 3, 1922 1,766,510 Gregory June 24, 1934 2,179,179 Fischel Nov. '7, 1939 2,369,505 Ward Feb. 13, 1945. 

